Enhancement of critical current density and irreversibility field by nano-carbon substitution in MgB2

Abstract

We have investigated the effect of nano-carbon doping on phase formation, critical current density, flux pinning and irreversibility field in MgB2−x bulk sample where x=0, 0.05, 0.1, 0.2 and 0.3. XRD results showed a systematic shift of lattice parameter a, which is attributed to carbon substitution, while the lattice parameter c almost did not change as the carbon content increased. Enhancement of magnetic Jc by two orders at 5K and 8T was observed for the sample of x=0.1, as the Jc(H) reached the value of >104 at 8T. In addition, the Hirr of the 5% doped carbon was enhanced from 4.9T to 5.8T as compared to the undoped sample. Boron substitution for carbon is proposed to be responsible for the enhancement of flux pinning.